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Linux prepares to axe legacy x32 hybrid mode — hybrid 32-bit/64-bit mode faces complete removal by 2027 due to low adoption
Linux developers are looking into retiring the x32 ABI that was introduced into the Linux kernel in 2012. Phoronix reports that Sebastian Andrezj Siewior of Lintronix has proposed removing the x32 ABI from the Linux kernel due to its obsolescence and lack of serious adoption since its debut. If no objections are raised, the x32 ABI will likely be removed from the Linux kernel by 2027.
x32 ABI was introduced to Linux in an effort to optimize the memory consumption of 64-bit programs. The application binary interface was designed to allow 64-bit processors and applications to operate in semi “64-bit/32-bit” hybrid mode. With x32 ABI, software is allowed access to the full 64-bit register file and data path but is restricted to using 32-bit pointers. For the uninitiated, a pointer is a binary number that keeps track of data that is held in system memory.
This ability allows the OS to use more than 4GB of RAM while keeping pointer sizes at just 4 bytes instead of 8 bytes (for 64-bit). This size difference is x32 ABI’s main selling point, as cutting the pointer size in half improved the amount of data that can fit in a CPU’s multiple caches and improved performance.
Despite its potential, x32 ABI also had several disadvantages. Using x32 ABI adds additional complexity for developers to deal with and requires compilers to support the feature. Arguably, its biggest technical problem relates to the fact that individual processes running with x32 ABI cannot take advantage of more than 4GB of memory due to the pointer sizes being limited to 32 bits.
That said, the nail in the coffin for x32 ABI is its lack of mainstream adoption by software developers as a whole. This was likely helped by the fact that x32 ABI was ever only implemented on Linux and was not ported to Windows or Mac. Sebastian Andrezj Siewior highlighted further issues in his proposal, noting that the better performance x32 ABI realized was not great enough for certain workloads to move to it and use it exclusively.
